1. Field of the Invention
The present invention relates to a coffee machine for producing and dispensing coffee-based beverages.
2. Background Art
Coffee, as a beverage, has always been widely used and prized; nowadays, in fact, it occurs in numerous varieties, which differ from one another both in the starting mixture, and in the method of extraction of the beverage.
In particular, espresso coffee is a beverage obtained instantaneously by using a coffee machine which passes hot water through a layer of ground coffee contained in an infusion chamber, generally a metal filter. The water which passes through the layer of coffee must be heated to a certain temperature and is subjected to a certain pressure, where the optimum pressure and temperature are selected also according to the starting mixture. Typically, the temperature of the water admitted into the infusion chamber is between around 88 and 98° C. and the pressure varies from around 0.8 to 1.5 bar in the initial dispensing period, rising then to around 9 bar during the extraction of the beverage.
As is known, among the items of equipment used in bars, hotels and restaurants and, even more, also among the items of equipment for domestic use, what is commonly termed an espresso coffee machine is in reality an apparatus which, besides espresso coffee, also provides many other services. With these machines it is in fact possible to dispense hot water for the production of infusions such as tea and camomile tea, to dispense superheated steam which, with its thermal and kinetic energy, makes it possible to heat the milk rapidly and to form the fine froth which characterizes cappuccino.
In the majority of machines for espresso coffee that are currently used, the boiler for heating the water is separate from the dispensing assembly and from the infusion chamber.
Italian Patent No. 1131532 describes a coffee machine which comprises a water supply circuit in which the flow of water is controlled by a pump, a boiler for obtaining steam under pressure, and at least one dispensing assembly equipped with a filter-holder into which coffee powder is inserted and measured. Each dispensing assembly comprises a mini-boiler equipped with self-contained thermal regulation and the water supply circuit extends in a manner suitable for supplying, in parallel, the boiler and each mini-boiler.
European Patent Application No. 1 360 918 discloses an espresso coffee machine having a plurality of dispensing units, connected to a source of cold water under pressure, and provided with a solenoid valve for shutting-off the water which is to be supplied, wherein each dispensing unit comprises a separate mini-boiler connected to the water source and provided with an electrical resistance element connected to electrical supply conductors by means of a separate switch and thermostat.
European Patent Application No. 1 882 433 describes a hydraulic circuit for a coffee machine in which an external water supply source and the dispensing device are placed in fluid communication with each other via a cold water pipe and a hot water pipe which provides heating means, wherein the cold water pipe and the hot water pipe join one another at a mixing point upstream of the dispensing device. In the body of the dispensing device of the machine a heat generator is arranged, separate from the heating means interposed upstream of the hot pipe, to compensate for the heat losses of the dispensing body which are due to dissipation into the external environment. Upstream of the mixing point, two solenoid valves are disposed respectively on the cold pipe and on the hot pipe. The solenoid valves are operated by control means which regulate the flow rate respectively of the respective pipes and therefore the temperature of the water which flows downstream of the mixing point.
The Applicant has observed that a system for controlling the temperature of the water sent to the coffee infusion chamber of the dispensing device, comprising a plurality of solenoid valves for regulating the temperature of the water supplied, increases not only the costs of production of the machine, but also those for maintaining same.
The Applicant has further observed that in a hydraulic system which provides for a dispensing device provided with a mini-boiler fed directly by the mains water system, although the volume of water contained in the mini-boiler is relatively limited, a certain time is however required to bring the water to the temperature suitable for the preparation of the coffee and this is with a relatively high consumption of electric power. For example, the electric power used to raise the temperature of the water from “ambient” temperature (for example 10-20° C.) at which the water leaves the mains water system, to the temperature necessary for the preparation of an espresso coffee (for example 90° C.), may be around 0.8-2.5 kW, depending also on the quantity of beverage to be dispensed, with a consequent high consumption of electric power.